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| United States Patent |
5,107,327
|
|
Nishimori
, et al.
|
April 21, 1992
|
Photosemiconductor device and epoxy resin composition for use in molding
photosemiconductor
Abstract
A photosemiconductor device and an epoxy resin composition for use in
molding a photosemiconductor used for the photosemiconductor device, the
photosemiconductor device comprises a photosemiconductor element molded
with a cured transparent epoxy resin composition, the cured transparent
epoxy resin composition having a refractive index distribution curve
characterized by the following (A), (B), and (C):
(A) the refractive index difference X between refractive index values (b)
and (c), which respectively are lower and higher than refractive index
value (a) corresponding to the maximum peak of the refractive index
distribution curve and respectively correspond to those points on the
refractive index distribution curve which have a relative height of 20
with the height of the maximum peak being taken as 100, is 0.0018 or less;
(B) the refractive index difference Y, which is the larger one of the
difference between the refractive index values (a) and (b) and the
difference between the refractive index values (a) and (c), is 0.0012 or
less; and
(C) in the case where the refractive index distribution curve has other
peak or peaks than the maximum peak corresponding to the refractive index
value (a), the refractive index difference Z, which is the largest one of
the differences between the refractive index value (a) and refractive
index values (d, . . . d.sub.n) corresponding to the other peak or peaks,
is 0.0010 or less.
| Inventors:
|
Nishimori; Syuuji (Osaka, JP);
Harada; Tadaaki (Osaka, JP);
Yamamoto; Yasuhiko (Osaka, JP);
Hiromori; Nobuyuki (Osaka, JP);
Yoshimura; Yasumori (Osaka, JP);
Muramatsu; Katsuya (Osaka, JP);
Shimada; Katsumi (Osaka, JP)
|
| Assignee:
|
Nitto Denko Corporation (Osaka, JP)
|
| Appl. No.:
|
553284 |
| Filed:
|
July 17, 1990 |
| Current U.S. Class: |
257/793; 174/52.2; 257/E31.117; 257/E31.127; 525/31; 525/481 |
| Intern'l Class: |
H01L 023/28; H01L 023/48; H01L 029/44; H01L 029/52 |
| Field of Search: |
357/72,74,73,70
174/52.2
|
References Cited
U.S. Patent Documents
| 4327369 | Apr., 1982 | Kaplan | 357/72.
|
| 4663190 | May., 1987 | Fujita et al. | 427/82.
|
| 4703338 | Oct., 1987 | Sagami et al. | 357/72.
|
| 4926239 | May., 1990 | Fujita et al. | 357/72.
|
Other References
Database WPIL, No. 88-115956, Derwent Publications Ltd. London, GB &
JP-A-63062363 (Nitto Electric Ind. K.K.).
Database WPI, No. 80-80854C, Derwent Publications Ltd., London GB, &
DD-A-143839 (VEB Pentacon Dresden).
Patent Abstracts of Japan, vol. 10, No. 137 (E-405)(2194) May 21, 1986, &
JP-A-61 001068 (Mitsubishi Denki K.K.) Jan. 7, 1986.
|
Primary Examiner: Hille; Rolf
Assistant Examiner: Ostrowski; David
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak & Seas
Claims
What is claimed is:
1. A photosemiconductor device comprising a photosemiconductor element
molded with a cured transparent epoxy resin composition, said cured
transparent epoxy resin composition having a refractive index distribution
curve characterized by the following (A), (B), and (C):
(A) a refractive index difference X between refractive index values (b) and
(c), which respectively are lower and higher than refractive index value
(a) corresponding to a maximum peak of said refractive index distribution
curve, and which respectively correspond to those points on said
refractive index distribution curve which have a relative height of 20,
with the height of said maximum peak being taken as 100, is 0.0018 or
less;
(B) a refractive index difference Y, which is the larger value of the
difference between said refractive index values (a) and (b) and the
difference between said refractive index values (a) and (c), is 0.0012 or
less; and
(C) with the proviso than when said refractive index distribution curve has
an additional peak or peaks other than said maximum peak corresponding to
said refractive index value (a), a refractive index difference Z, which is
the largest value of the differences between said refractive index value
(a) and refractive index values (d, . . . d.sub.n) corresponding to said
other peak or peaks, is 0.0010 or less.
2. A photosemiconductor device as claimed in claim 1, wherein said
refractive index difference Z in requirement (C) is 0.0003 or less.
3. A photosemiconductor device comprising a photosemiconductor element and
a molding resin in which said photosemiconductor element is molded, said
molding resin being one formed by curing a B-stage epoxy resin composition
for use in molding photosemiconductors, said B-stage epoxy resin
composition comprising an epoxy resin, a hardener, and a curing
accelerator as constituent ingredients, wherein said constituent
ingredients are mixed with each other uniformly to the molecular level;
and said cured B-stage transparent epoxy resin composition has a
refractive index distribution curve characterized by the following (A),
(B), and (C):
(A) a refractive index difference X between refractive index values (b) and
(c), which respectively are lower and higher than refractive index value
(a) corresponding to a maximum peak of said refractive index distribution
curve, and which respectively correspond to those points on said
refractive index distribution curve which have a relative height of 20,
with the height of said maximum peak being taken as 100, is 0.0018 or
less;
(B) a refractive index difference Y, which is the larger value of the
difference between said refractive index values (a) and (b) and the
difference between refractive index values (a) and (c), is 0.0012 or less;
and
(C) with the proviso that when said refractive index distribution curve has
an additional peak or peaks other than said maximum peak corresponding to
said refractive index value (a), a refractive index difference Z, which is
the largest value of the differences between said refractive index value
(a) and refractive index values (d, . . . d.sub.n) corresponding to said
other peak or peaks, is 0.0010 or less.
4. An epoxy resin composition for use in molding photosemiconductors,
produced by a process comprising: dissolving into an organic solvent a
B-stage epoxy resin composition comprising an epoxy resin, a hardener, and
a curing accelerator, and removing the organic solvent until the amount of
said organic solvent remaining is 3% by weight or less based on the total
amount of said B-stage epoxy resin composition, and wherein said B-stage
epoxy resin composition has a refractive index distribution curve
characterized by the following (A), (B), and (C):
(A) a refractive index difference X between refractive index values (b) and
(c), which respectively are lower and higher than refractive index value
(a) corresponding to a maximum peak of said refractive index distribution
curve, and which respectively correspond to those points on said
refractive index distribution curve which have a relative height of 20,
with the height of said maximum peak being taken as 100, is 0.0018 or
less;
(B) a refractive index difference Y, which is the larger value of the
difference between said refractive index values (a) and (b) and the
difference between said refractive index values (a) and (c), is 0.0012 or
less; and
(C) with the proviso that when said refractive index distribution curve has
an additional peak or peaks other than said maximum peak corresponding to
said refractive index value (a), a refractive index difference Z, which is
the largest value of the differences between said refractive index value
(a) and refractive index values (d, . . . d.sub.n) corresponding to said
other peak or peaks, is 0.0010 or less.
5. An epoxy resin composition for use in molding photosemiconductors,
produced by a process comprising: dissolving an epoxy resin, a hardener,
and a curing accelerator into an organic solvent, and removing said
organic solvent until the amount of said organic solvent remaining is 3%
by weight or less based on the total amount of said B-stage epoxy resin
composition, and wherein said B-stage epoxy resin composition has a
refractive index distribution curve characterized by the following (A),
(B), and (C):
(A) a refractive index difference X between refractive index values (b) and
(c), which respectively are lower and higher than refractive index value
(a) corresponding to a maximum peak of said refractive index distribution
curve, and which respectively correspond to those points on said
refractive index distribution curve which have a relative height of 20,
with the height of said maximum peak being taken as 100, is 0.0018 or
less;
(B) a refractive index difference Y, which is the larger value of the
difference between said refractive index values (a) and (b) and the
difference between said refractive index values (a) and (c), is 0.0012 or
less; and
(C) with the proviso than when said refractive index distribution curve has
an additional peak or peaks other than said maximum peak corresponding to
said refractive index value (a), a refractive index difference Z, which is
the largest value of the differences between said refractive index value
(a) and refractive index values (d, . . . d.sub.n) corresponding to said
other peak or peaks, is 0.0010 or less.
6. An epoxy resin composition as claimed in claim 5, further comprising
heating said dissolved epoxy resin, hardener, and curing accelerator to
allow the curing reaction of the epoxy resin to proceed.
7. An epoxy resin composition as claimed in claim 5, wherein said organic
solvent is removed without allowing said B-stage epoxy resin to undergo a
reaction, and then allowing residual epoxy resin composition to cure.
8. An epoxy resin composition as claimed in claim 5, wherein said B-stage
epoxy resin is selected from the group consisting of bisphenol A epoxy
resins and bisphenol F epoxy resins, and said hardener is selected from
the group consisting of phthalic anhydride and tetrahydrophthalic
anhydride.
9. An epoxy resin composition as claimed in claim 4, wherein the amount of
said organic solvent remaining is 1.5% by weight or less based on the
total amount of said B-stage epoxy resin composition.
10. An epoxy resin composition as claimed in claim 5, wherein the amount to
the organic solvent remaining is 1.5% by weight or less based on the total
amount of said B-stage epoxy resin composition.
11. An epoxy resin composition as claimed in claim 4, wherein the amount of
the organic solvent remaining is 0.05% by weight or less based on the
total amount of said B-stage epoxy resin composition.
12. An epoxy resin composition as claimed in claim 5, wherein the amount of
the organic solvent remaining is 0.05% by weight or less based on the
total amount of said B-stage epoxy resin composition.
Description
FIELD OF THE INVENTION
The present invention relates to a photosemiconductor device free of
optical unevenness and an epoxy resin composition for use in molding a
photosemiconductor used for the photosemiconductor device.
BACKGROUND OF THE INVENTION
Conventionally, photoreceiving elements such as solid stat image forming
elements have generally been enclosed in ceramic packages in such a manner
as to result in some spaces between the elements and the packages, to
produce photosemiconductor devices. These ceramic packages, however, are
undesirable because the constituent materials therefor are relatively
expensive and large-scale production thereof is inefficient. Therefore,
resin moldings for plastic packages have been studied. Of such resin
molding techniques, molding with epoxy resin compositions in particular
have been extensively studied. Such epoxy resin compositions are obtained
by melt-mixing epoxy resins, hardeners, curing accelerators and other
additives with heating.
However, the thus-obtained epoxy resin compositions for use in the molding
of photosemiconductors are undesirable because the dispersion of each of
the epoxy resin, hardener, and curing accelerator is insufficient so that
these components have not been mixed uniformly at the molecular level. For
this reason, if transfer molding, for example, is carried out using such
an epoxy resin composition for photosemiconductor molding, the following
problems result.
In producing this resin molding, when the epoxy resin composition for
photosemiconductor molding is cured, the curing reaction proceeds at
higher rates in some parts and at lower rates in other parts because the
dispersion of each component in the epoxy resin composition is not uniform
when viewed on a molecular level. Such uneven rates of the curing reaction
result in unevenness in the density of the cured molding resin, and this
causes the refractive index of the molding resin to vary over a wide
range. The molding resin has optical unevenness which appear as a striped
pattern extending in the direction of the resin flow. If, for example, an
area sensor of a solid state image forming element is molded with a
conventional epoxy resin composition for photosemiconductor molding by the
method described above and intense parallel light rays are allowed to
strike upon the molded area sensor with an iris diaphragm having f-32,
such optical unevenness in the molding resin as above causes the resulting
image to have a striped pattern.
SUMMARY OF THE INVENTION
Under these circumstances, the present inventors conducted a series of
extensive studies in order to eliminate optical unevenness from the cured
resins obtained from epoxy resin compositions for use in
photosemiconductor molding. As a result, it was found that the formation
of optical unevenness is greatly affected by the refractive index
distribution of the cured resin. Further studies have been made with
regard to refractive index distribution and, as a result, it has now been
found that a cured resin with no optical unevenness ca be obtained by
making the refractive index distribution curve of the cured resin sharp so
as to satisfy the specific requirements (A), (B), and (C) described later.
The present invention has been completed based on the above finding.
Accordingly, an object of the present invention is to provide a
photosemiconductor device free from optical unevenness.
Another object of the present invention is to provide an epoxy resin
composition for use in molding a photosemiconductor element to produce the
above photosemiconductor device.
Other objects and effects of the present invention will be apparent from
the following description.
The present invention relates to a photosemiconductor device comprising a
photosemiconductor element molded with a cured transparent epoxy resin
composition, the cured transparent epoxy resin composition having a
refractive index distribution curve characterized by the following (A),
(B), and (C):
(A) the refractive index difference X between refractive index values (b)
and (c), which respectively are lower and higher than refractive index
value (a) corresponding to the maximum peak of the refractive index
distribution curve and respectively correspond to those points on the
refractive index distribution curve which have a relative height of 20
with the height of the maximum peak being taken as 100, is 0.0018 or less;
(B) the refractive index difference Y, which is the larger one of the
difference between the refractive index values (a) and (b) and the
difference between the refractive index values (a) and (c), is 0.0012 or
less; and
(C) with the proviso that the refractive index distribution curve has other
peak or peaks than the maximum peak corresponding to the refractive index
value (a), the refractive index difference Z, which is the largest one of
the differences between the refractive index value (a) and refractive
index values (d, . . . d.sub.n) corresponding to the other peak or peaks,
is 0.0010 or less.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a refractive index distribution curve having a maximum peak only;
FIG. 2 is a refractive index distribution curve having the maximum peak and
another peak;
FIG. 3 is a schematic view illustrating the flow of a conventional,
photosemiconductor-molding epoxy resin composition being used in transfer
molding;
FIG. 4 is a schematic view illustrating the resin composition flow in the
pivotal part of the transfer molding machine shown in FIG. 3;
FIG. 5 is a vertical sectional view of a photosemiconductor device molded
in an epoxy resin composition of this invention for photosemiconductor
molding;
FIG. 6 is a diagrammatic view illustrating the principle in a refractive
index-measuring apparatus; and
FIGS. 7, 8, 9, 10, 11, 12, and 13 show refractive index distribution curves
.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described below in detail.
In the photosemiconductor device of the invention, a photosemiconductor
element is molded in a cured transparent epoxy resin composition which
satisfies the above requirements (A), (B) and (C).
The cured resin satisfying the requirements (A), (B), and (C) has a
narrower refractive index distribution, i.e., a sharper refractive index
distribution curve, than the cured resins obtained from conventional epoxy
resin compositions.
The requirements (A), (B), and (C) are explained below with reference to
the drawings. In FIG. 1, which is a bell-shaped refractive index
distribution curve of one example of the cured transparent epoxy resin
composition employed in the present invention, K indicates the refractive
index distribution curve, (a) indicates the refractive index value
corresponding to the maximum peak of the distribution curve, (b) and (c)
indicate refractive index values respectively corresponding to those
points on the refractive index distribution curve which have a relative
height of 20 with the height of the maximum peak being taken as 100 and
which respectively are on the left and right of the maximum peak, X is the
refractive index difference between the refractive index values (b) and
(c), and Y is the refractive index difference which is the larger one of
the difference between the refractive index value (a) corresponding to the
maximum peak and the refractive index value (b) and the difference between
the refractive index values (a) and (c) (in the figure, Y is the
difference between (a) and (c) because this difference is larger than the
difference between (a) and (b)).
Even if the refractive index distribution curve has a peak (a') other than
the maximum peak (a), as shown in FIG. 2, no optical unevenness results as
long as the refractive index distribution curve satisfies the above
requirements (A) and (B). However, in the case where the picture element
numbers for the present-day solid state image forming elements are
increased greatly or such a function that a refractive index difference is
emphasized by means of a microlens is imparted to photosemiconductor
devices, the presence of a peak (a') other than the maximum peak (a) may
cause a problem. Even in such a case where a refractive index distribution
curve has two or more peaks, the cured resin can be made applicable to
future solid state image forming elements which may possibly have greatly
increased picture element numbers, without causing problems ascribable to
optical unevenness, by regulating the refractive index difference Z, which
is the largest one of the differences between the refractive index value
(a) corresponding to the maximum peak and refractive index value(s)
corresponding to the other peak(s) (in FIG. 2, Z is the refractive index
difference between (a) and (a')), at 0.0010 or less, preferably at 0.0003
or less.
The refractive index curves shown in FIGS. 1 and 2 referred to above can be
obtained by measurement with a refractive index-measuring apparatus
utilizing the principle shown in FIG. 6. In FIG. 6, F indicates an
interference filter, SL a spectral illuminant lamp, S.sub.1 an inlet slit,
S.sub.2 an outlet slit, L.sub.1 a collimator lens, L.sub.2 a telemeter
lens, P a V-block prism, SM a sample to be tested, P.M a photomultiplier,
and N a telemeter part.
For measurement with this refractometer, a cured transparent epoxy resin
composition is formed, for example, into a cubic sample SM, two adjacent
sides of the cubic sample are polished by buffing so as to have a surface
roughness of 1.5 .mu.m or less, and this sample is set on the V-block
prism P having a V-shaped depression with the polished sides of the sample
being in contact with the V-shaped depression walls. Then, light is
emitted from the illuminant SL. The light emitted from the illuminant SL
is converted to monochromatic light by the interference filter F, and the
monochromatic light passes through the inlet slit S.sub.1 and then
converted to parallel rays of light by the collimator lens L.sub.1. The
parallel light rays pass through the V-block prism P, the sample SM, and
the V-block prism P in this order, while the parallel light rays are being
polarized upward and downward relative to the light axis due to the
difference in refractive index between the V-block prism P and the sample
SM. The telemeter part N, equipped with the telemeter lens L.sub.2, the
outlet slit S.sub.2, and the photomultiplier P.M, oscillates as shown by
the arrows by means of a pulse motor (not shown) and receives the
polarized light at each position in the oscillation movement, and the
amount of the received light is indicated on a display (not shown) as the
amount of energy. For this measurement, the relationship between
refractive index and each angle in the above oscillation movement has been
determined beforehand. Therefore, the amount of light received at a given
angle means the amount of light refracted at an angle corresponding to
that given angle.
Examples of this refractive index-measuring apparatus includes devices
produced and marketed by Karunew Optics Company, Japan under the trade
name of Automatic Refractometer KPR-200. The measurement of refractive
index in the present invention is made by means of this refractometer with
sodium D-line (587.6 nm) being used as the measuring light.
The cured transparent epoxy resin composition free of optical unevenness is
one whose refractive index distribution curve obtained by the method as
described above is sharp and satisfies the requirements (A), (B), and (C)
described hereinabove.
An epoxy resin composition which can cure into a resin having such a sharp
refractive index distribution curve may be produced, for example, by
uniformly dispersing each of the constituent ingredients in the epoxy
resin composition.
Examples of the technique of uniformly dispersing ingredients to produce an
epoxy resin composition for use in photosemiconductor molding include: (1)
a method in which a conventional powdery epoxy resin composition for
molding use which has been made in the B-stage (semi-cured state) is mixed
sufficiently with an organic solvent to dissolve each component, and then
the organic solvent is evaporated; (2) a method in which raw ingredients
such as an epoxy resin, a hardener, a curing accelerator, and others are
mixed with and uniformly dissolved in an organic solvent, the resulting
solution is heated so as to result in a B-stage composition, and then the
solvent is evaporated; and (3) a method in which the same solution as that
obtained in (2) above is prepared, subsequently the solvent is evaporated,
and then the residue is heated mildly to form a B-stage composition.
In the above methods, since an epoxy resin composition or raw materials
therefor are once dissolved in an organic solvent, it is possible, by the
filtration of these solutions, to easily remove fine foreign substances
such as dust particles, the removal of which has so far been impossible.
Furthermore, even if the refractive index distribution curve of a cured
resin to be obtained from the resulting epoxy resin composition has a peak
(a') other than the maximum peak (a), the other peak can be weakened by
reducing the epoxy resin composition to a uniformly mixed fine powder,
thereby giving a bell-shaped distribution curve having the maximum peak a
only as shown in FIG. 1. The term fine powder herein normally means a
powder in which particles having maximum particle-diameters of 30 .mu.m or
less, preferably 10 .mu.m or less, comprise 90 wt % or more of the powder.
In the above method (1), a B-stage (semi-cured) epoxy resin composition is
prepared by mixing the above-mentioned ingredient. As the method for
mixing the ingredients, a partial reaction method (semi-curing method) and
melt-mixing method are generally used. The degree of reaction of the
B-stage epoxy resin composition is generally such an extent that the
gelation time of the resin composition at 150.degree. C. be from 10 to 70
seconds, and preferably from 10 to 40 seconds. Next, the B-stage epoxy
resin composition is uniformly dissolved in an organic solvent. By this
procedure, the ingredients of the resin composition are mixed with each
other uniformly on the molecular level. The organic solvent is then
removed by evaporation from the solution, and the residue is cooled to
room temperature and pulverized by a conventional method. The pulverized
resin composition is stamped into tablets if desired.
The degree of reaction of the thus-obtained final epoxy resin composition
generally proceeds to such an extent that a transfer molding process can
be carried out and that the gelation time at 150.degree. C. is from 10 to
50 seconds, and preferably from 10 to 40 seconds. In the above method, the
resin composition may be heated after removing the organic solvent in
order to adjust the viscosity of the resin composition or the like. At
this time, if the resin composition is heated vigorously, unevenness of
the curing degree due to unevenness of the reaction rate develops.
Therefore, the heating of the resin composition is preferably carried out
gradually at a low temperature so that the gelation time at 150.degree. C.
is not reduced to less than 20 seconds.
In the above method (2), the ingredients are first dissolved in an organic
solvent. By this procedure, the ingredients of the resin composition are
mixed with each other uniformly on the molecular level. The resulting
solution is heated to initiate the curing reaction so as to convert the
resin composition to the B-stage. The organic solvent is then removed by
evaporation from the solution, and the residue is cooled to room
temperature and pulverized by a conventional method. The pulverized resin
composition is stamped into tablets if desired.
In this method, the ingredients may be heated simultaneously with
dissolving in the organic solvent but not heated after completion of
dissolution. Alternatively, the B-stage resin composition may be further
heated to heighten the degree of curing. In this method, while the resin
composition may be heated after removing the organic solvent to adjust the
viscosity or the like, the heating is preferably carried out gradually at
a low temperature so that the gelation time at 150.degree. C. is not
reduced to less than 20 seconds.
The degree of reaction of the thus-obtained final product generally
proceeds to such an extent that the gelation time at 150.degree. C. is
from 10 to 70 seconds, and preferably from 10 to 40 seconds. At this time,
the extent of gelation after starting evaporation of the organic solvent
is preferably controlled such that the gelation time at 150.degree. C. is
not less than 20 seconds.
In the above method (1) and (2), one, or two or more kinds of each
ingredient may be used. The term "one kind" used herein includes, in the
case of epoxy resins for example, bisphenol A type and bisphenol F type
which have the same skeleton and are classified as the bisphenol type, and
in the case of hardener, phthalic anhydride and tetrahydrophthalic
anhydride which have the same skeleton and are classified as the phthalic
acid type.
In the above method (3), one kind of the epoxy resin and one kind of
hardener are dissolved in an organic solvent. The organic solvent is
removed by evaporation from the resulting solution, and the residue is
subjected to low temperature heating (low temperature aging) so as to
convert the residue into the B-stage. In this method, because one kind of
the epoxy resin and one kind of hardener are used, only one kind of cured
product is produced. Thus, unevenness of curing degree does not appear and
optical unevenness is not formed.
In this method, if the low temperature aging is carried out gradually at a
low temperature so that the gelation time at 150.degree. C. is not less
than 20 seconds, optical unevenness is substantially reduced even though
two or more kinds of each ingredient are used.
The degree of reaction of the thus-obtained final product generally
proceeds to such an extent that the gelation time at 150.degree. C. is
from 10 to 70 seconds, and preferably from 10 to 40 seconds. At this time,
the extent of gelation after starting evaporation of the organic solvent
is preferably controlled such that the gelation time at 150.degree. C.
does not lower than 20 seconds.
The epoxy resin composition for photosemiconductor molding to be used for
producing the photosemiconductor device of the present invention is one
which is obtained by use of an epoxy resin, a hardener, and a curing
accelerator, and contains no inorganic fillers such as silica powder.
As the epoxy resin, conventionally known epoxy resins may be used without
any particular limitation as long as the epox used and the resulting cured
composition are less apt to undergo discoloration. Examples of such epoxy
resins include bisphenol A epoxy resins, bisphenol F epoxy resins,
phenol-novolac epoxy resins, alicyclic epoxy resins,
heterocycle-containing epoxy resins such as triglycidyl isocyanurate an-d
hydantoin epoxies, hydrogenated bisphenol A epoxy resins, aliphatic epoxy
resins, glycidyl ether epoxy resins, and the like. These may be used alone
or in combination.
As the hardener, known hardeners for epoxy resins can be used without any
particular limitation. However, acid anhydrides are advantageous in that
they are less apt to cause discoloration of the resin composition during
or after cure. Examples of such acid anhydrides include phthalic
anhydride, maleic anhydride, trimellitic anhydride, pyromellitic
anhydride, hexahydrophthalic anhydride, tetrahydrophthalic anhydride,
methylnadic anhydride, nadic anhydride, glutaric anhydride, and the like.
Other examples of the hardener include amine-type hardeners such as
m-phenylenediamine, dimethyldiphenylmethane, diaminodiphenyl sulfone,
m-xylenediamine, tetraethylenepentamine, diethylamine, propylamine, and
the like, and further include phenolic resin-type hardeners. Any of these
may be employed.
In the present invention, the epoxy resin is at least one of bisphenol A
epoxy resin and bisphenol F epoxy resin, and the hardener is at least one
of phthalic anhydride and tetrahydrophthalic anhydride.
Examples of the curing accelerator include tertiary amines, imidazole and
its derivatives, metal salts of carboxylic acids, phosphorus compounds,
and the like.
Besides the above-described ingredients, conventionally known additives
such as anti-discoloring agents, modifiers, anti-deteriorating agents,
mold-release agents, etc. may be incorporated, if required and necessary,
into the epoxy resin composition of this invention for photosemiconductor
molding.
As the anti-discoloring agent, conventionally known ones may be mentioned,
such as phenolic compounds, amine-type compounds, organosulfur compounds,
phosphine-type compounds, and the like.
The organic solvent to be used for producing the epoxy resin composition is
not particularly limited as long as it is capable of completely dissolving
B-stage epoxy resin compositions for photosemiconductor molding. Examples
of the organic solvent include hydrocarbons such as toluene and xylene,
halogenated hydrocarbons such as dichloromethane, 1,1,1-trichloroethane
and 1,1,2-trichloroethane, ethers such as diethyl ether, dioxane and
tetrahydrofuran, ketones such as acetone, methyl ethyl ketone and diethyl
ketone, mixed solvents composed of two or more thereof, and the like.
Neither the mixing ratio of the organic solvent to the epoxy resin
composition for photosemiconductor molding or the temperature for mixing
is particularly limited, as long as the epoxy resin composition for
photosemiconductor molding can be completely dissolved.
Generally however, the amount of the organic solvent used is preferably
from 1 to 50 times by weight, more preferably from 1 to 10 times by
weight, the amount of the B-stage epoxy resin composition for
photosemiconductor molding. The mixing temperature is preferably kept at
100.degree. C. or lower because too high a temperature results in gelation
of the epoxy resin composition for photosemiconductor molding.
Methods for removing the organic solvent in the above processes are not
particularly limited. For example, there may be employed a method in which
the solvent is removed under reduced pressure at ordinary temperature or
with heating according to need, or a method in which the solvent is
removed by freeze drying under vacuum.
It is preferred that the amount of the organic solvent remaining unremoved
should be 3% by weight or less based on the total amount of the epoxy
resin composition for photosemiconductor molding. The content of the
remaining organic solvent in the epoxy resin composition is more
preferably 1.5% by weight or less, and particularly preferably 0.05% by
weight or less. If the content of the remaining organic solvent exceeds 3%
by weight, the epoxy resin composition for photosemiconductor molding
tends to have a very short pot life and the cured composition tends to
have a lowered glass transition temperature and hence an increased linear
expansion coefficient, so that the molding resin may have impaired
moisture and heat cycle resistance.
The epoxy resin composition for photosemiconductor molding obtained by the
method described above is in such a state that all the components have
been mixed with each other uniformly to the molecular level. Therefore,
the refractive index distribution curve of the cured composition is sharp,
so that the curd composition has no optical unevenness. Furthermore, since
all the components are dissolved in an organic solvent during the
production process and, hence, can be easily purified by suction
filtration under reduced pressure or by filtration under pressure using an
ordinary filter paper or the like, gel-like aggregates and foreign
substances including fine dust particles present in the resin composition
can be easily removed which have so far been difficult to remove.
It is preferable that the epoxy resin composition for photosemiconductor
molding should be optically transparent since it is to be used in the
resin molding of photosemiconductors such as photoreceiving elements. The
term "transparent" used herein means that the cured resin obtained from
the epoxy resin composition for photosemiconductor molding has a
transmittance of generally 90% or higher, preferably 95% or higher, more
preferably 98% or higher, as measured at 600 nm with the cured resin
thickness being 1 mm.
The meaning of "ingredients being mixed with each other uniformly to the
molecular level" is as follows. The resin composition is transfer molded
at 150.degree. C. for 6 minutes and then hardened at 150.degree. C. for 3
hours. The hardened resin composition is taken out from the runner portion
of the molding die, and formed into a flat plate (thickness: 3.0 mm,
width: 5 mm) having a branch perpendicular to the flat plate, the surface
of which is polished to have a surface roughness of 1.5 .mu.m or less. The
plate of the cured resin composition is equipped on a solid state image
forming element (1/2 inch, 380,000 picture elements). Intense parallel
light rays having a luminous intensity of 10 candelas are allowed to
strike the image forming element with an iris diaphragm of f-32. If no
striped interference pattern is observed the composition is "mixed
uniformly on the molecular level".
Molding of photoreceiving elements or other photosemiconductors with the
epoxy resin composition is not particularly limited, and can be carried
out by known molding techniques such as, for example, ordinary transfer
molding. In practicing the transfer molding, a molding resin composition
in a powder form is normally used after being tableted at ordinary
temperature.
In the transfer molded resin composition of the present invention, because
the ingredients are mixed with each other uniformly to the molecular
level, curing unevenness and optical unevenness are not produced although
such unevenness is formed in conventional resin compositions.
The photosemiconductor device thus obtained, for example, has a structure
as shown in FIG. 5, in which an image-pickup solid element 13 as a
photoreceiving element is mounted on a bonding pad 11 through an adhesive
12, and a color filter 15 is bonded to the upper side of the
photoreceiving element by means of a transparent adhesive 14, with this
assembly being resin-molded in an epoxy resin composition 16 for
photosemiconductor molding. The color filter 15 has been provided in order
to obtain color images, and is unnecessary for monochromatic images. In
the figure, numeral 17 denotes a glass plate, 18 a bonding wire, and 19 a
lead frame.
Since this photosemiconductor device has been resin-molded in a
photosemiconductor-molding epoxy resin composition in which all the
components thereof have been mixed uniformly to the molecular level, the
refractive index distribution curve of the molding resin 16 is sharp, so
that the molding resin 16 has no optical unevenness. Therefore, images
obtained by operating this device are free from striped patterns
ascribable to optical unevenness and black spots due to inclusion from
foreign particles. The freedom of optical unevenness has been ascertained
with photosemiconductor devices obtained by regulating the thickness l of
the molding resin over the color filter 15 at ordinary values, i.e., 0.5
to 2 mm.
As described above, the photosemiconductor device of the present invention
is free of optical unevenness because the refractive index distribution
curve of the cured transparent epoxy resin composition is characterized by
(A), (B), and (C) described hereinabove. Furthermore, in the case where
the cured transparent epoxy resin is obtained from an epoxy resin
composition which has undergone a dissolution in an organic solvent,
foreign substances can be removed from the resin composition by
filtration, so that the cured resin can be made free of gel-like
aggregates and foreign substances, such as fine dust particles, present in
the resin composition, although these impurities have so far been
difficult to remove. Thus, the resin composition can be of high quality.
Therefore, such a high-quality epoxy resin composition is used for
resin-molding of a photoreceiving element such as solid state image
forming element or the like to produce a photosemiconductor device of the
present invention, the images formed by the photosemiconductor device are
free from striped patterns ascribable to optical unevenness of molding
resin or black spots ascribable to foreign substances present in molding
resin. That is, the photosemiconductor device of the present invention,
although being of a resin-molded type, has high performance that is equal
to or higher than those of ceramic-packaged types.
The present invention will be explained below in more detail by reference
to the following Examples and Comparative Examples, but the Examples
should not be construed to be limiting the scope of the invention.
Hereinafter, all parts are by weight.
EXAMPLE 1 TO 4 AND COMPARATIVE EXAMPLES 1 TO 3
For use in the Examples and Comparative Examples, epoxy resin compositions
A to G were prepared beforehand by the methods given below in which the
six formulations shown in Table 1 were used. In Table 1, the formulations
are indicated in terms of part by weight.
TABLE 1
______________________________________
Hardener
Epoxy resin tetrahydro-
Formu- Epikote Triglycidyl phthalic
lation 1001*.sup.1
isocyanurate*.sup.2
anhydride*.sup.3
Catalyst*.sup.4
______________________________________
1 75 25 52.0 0.3
2 75 25 51.9 0.3
3 75 25 51.8 0.3
4 75 25 51.7 0.3
5 75 25 51.4 0.3
6 75 25 51.0 0.3
______________________________________
Note:
*.sup.1 Manufactured by Yuka Shell Epoxy K.K., Japan
*.sup.2 Manufactured by Nissan Chemical Industries, Ltd., Japan
*.sup.3 Manufactured by Hitachi Chemical Co., Ltd., Japan
*.sup.4 "2E4MZ" manufactured by Shikoku Chemical Co., Ltd., Japan
Epoxy Resin Composition A
The ingredients shown under formulation 1 in Table 1 were melt-mixed with
heating in the respective proportions shown in the table, and then the
mixture was allowed to undergo curing reactions of the epoxy resins,
thereby preparing a B-stage epoxy resin composition for photosemiconductor
molding which composition had a gelation time as measured at 150.degree.
C. of 30 seconds. This B-stage epoxy resin composition for
photosemiconductor molding was completely dissolved in the organic solvent
whose kind and amount are shown in Table 2 given later, and then the
solvent was removed under reduced pressure, while the solution was being
heated at 45.degree. C. The resulting residue was reduced to powder to
obtain photosemiconductor-molding epoxy resin composition A in a powder
form (for Example 1) having the residual organic solvent content as shown
in Table 2 and a gelation time as measured at 150.degree. C. of 25
seconds.
Epoxy Resin Composition B
Two compositions were prepared according to formulations 1 and 3,
respectively, as shown in Table 1. Each of the two compositions was
allowed to undergo curing reactions of the epoxy resins thereby to
prepare, from each composition, a B-stage epoxy resin composition for
photosemiconductor molding which composition had a gelation time as
measured at 150.degree. C. of 30 seconds. 50 Parts each of the
thus-prepared two kinds of B-stage epoxy resin compositions for
photosemiconductor molding were blended with each other, and the blend was
mixed with and completely dissolved in the organic solvent whose kind and
amount are shown in Table 2. The solvent was then removed under reduced
pressure, while the solution was being heated at 45.degree. C. The
resulting residue was reduced to powder to obtain
photosemiconductor-molding epoxy resin composition B in a powder form (for
Example 2) having the residual organic solvent content as shown in Table 2
and a gelation time as measured at 150.degree. C. of 25 seconds. Epoxy
Resin Composition C
The ingredients shown under formulation 2 in Table 1 were melt-mixed with
heating, and then the mixture was allowed to undergo curing reactions of
the epoxy resins, thereby preparing a B-stage epoxy resin composition for
photosemiconductor molding which composition had a gelation time as
measured at 150.degree. C. of 30 seconds. This B-stage epoxy resin
composition for semiconductor molding was mixed with and completely
dissolved in the organic solvent whose kind and amount are shown in Table
2. The solvent was then removed under reduced pressure, while the solution
was being heated at 45.degree. C. The resulting residue was reduced to
powder to obtain photosemiconductor-molding epoxy resin composition in a
powder form having the residual organic solvent content as shown in Table
2 and a gelation time as measured at 150.degree. C. of 25 seconds. 40
Parts of this epoxy resin composition was dryblended with 60 parts of the
above-described epoxy resin composition A to obtain
photosemiconductor-molding epoxy resin composition C (for Example 3).
Epoxy Resin Composition D
The ingredients shown under formulation 4 in Table 1 were melt-mixed with
heating, and then the mixture was allowed to undergo curing reactions of
the epoxy resins, thereby preparing a B-stage epoxy resin composition for
photosemiconductor molding which composition had a gelation time as
measured at 150.degree. C. of 30 seconds. This B-stage epoxy resin
composition for photosemiconductor molding was mixed with and completely
dissolved in the organic solvent whose kind and amount are shown in Table
2. The solvent was then removed under reduced pressure, while the solution
was being heated at 45.degree. C. The resulting residue was reduced to
powder to obtain photosemiconductor-molding epoxy resin composition in a
powder form having the residual organic solvent content as shown in Table
2 and a gelation time as measured at 150.degree. C. of 25 seconds. 40
Parts of this epoxy resin composition was dryblended with 60 parts of the
above-described epoxy resin composition A to obtain
photosemiconductor-molding epoxy resin composition D (for Example 4).
Epoxy Resin Composition E
The ingredients shown under formulation 5 in Table 1 were melt-mixed with
heating without using an organic solvent, and then the mixture was allowed
to undergo curing reactions of the epoxy resins. The resulting mixture was
reduced to powder to obtain photosemiconductor-molding epoxy resin
composition E in a powder form (for Comparative Example 1) having a
gelation time as measured at 150.degree. C. of 25 seconds.
Epoxy Resin Composition F
The ingredients shown under formulation 5 in Table 1 were melt-mixed with
heating, and then the mixture was allowed to undergo curing reactions of
the epoxy resins, thereby preparing a B-stage epoxy resin composition for
photosemiconductor molding which composition had a gelation time as
measured at 150.degree. C. of 30 seconds. This composition was reduced to
powder. 35 Parts of the thus-obtained powdery epoxy resin composition was
dryblended with 65 parts of the above-described composition A to obtain
epoxy resin composition F (for Comparative Example 2).
Epoxy Resin Composition G
The ingredients shown under formulation 6 in Table 1 were melt-mixed with
heating, and then the mixture was allowed to undergo curing reactions of
the epoxy resins, thereby preparing a B-stage epoxy resin composition for
photosemiconductor molding which composition had a gelation time as
measured at 150.degree. C. of 30 seconds. This composition was reduced to
powder. 20 Parts of the thus-obtained powdery epoxy resin composition was
dryblended with 80 parts of the above-described epoxy resin composition A
to obtain epoxy resin composition G (for Comparative Example 3).
TABLE 2
__________________________________________________________________________
Example Comparative Example
1 2 3 4 1 2 3
__________________________________________________________________________
Epoxy resin composition
A B C D E F G
(part by weight)
Organic solvent
500 500 500 500 -- -- --
(dichloromethane)
(part by weight)
Residual organic
1 1 1 1 -- 0.65
0.80
solvent content (wt %)
Refractive index
0.0015
0.0018
0.0015
0.0015
0.0021
0.0018
0.0018
difference X
Refractive index
0.0010
0.0010
0.0010
0.0010
0.0010
0.0013
0.0012
difference Y
Refractive index
-- -- 0.0002
0.0006
-- 0.0008
0.0011
difference Z
Optical unevenness A
none none none none present
present
present
Optical unevenness B
none slightly
none slightly
present
present
present
present present
__________________________________________________________________________
(Refractive Index Measurement)
Each of the seven kinds of powdery epoxy resin compositions (A to G)
obtained by the methods described above were formed into tablets. Each
tableted composition was subjected to transfer molding at 150.degree. C.
for 6 minutes to form a cube, which was then cured at 150.degree. C. for 3
hours. Thus, seven cured cubes each measuring 1.times.1.times.1 cm were
prepared from the seven kinds of compositions. With respect to each of
these cured cubes, two adjacent sides were polished by buffing so that the
polished surfaces had surface roughnesses of 1.5 .mu.m or less. The
thus-obtained cubic samples (A to G) were examined for refractive index
distribution by means of a refractometer (Automatic Refractometer KPR-200
manufactured by Karunew Optics Company).
The results of the refractive index measurement on these samples A to G are
shown in FIGS. 7 to 13, respectively; samples A to D are for Examples,
while samples E to G are for Comparative Examples.
It is apparent, from the refractive index distribution curves for samples A
to D as shown in FIGS. 7 to 10 and from the values of X, Y, and Z in Table
2, that samples A to D satisfy requirements (A), (B), and (C) which are
essential in the present invention. In particular, in the case of samples
C and D, the refractive index distribution curves as shown in FIGS. 9 and
10 have peaks other than the maximum peaks, but the refractive index
differences Z between the refractive index value (a) corresponding to the
maximum peak and the refractive index value (a') corresponding to the
other peak are within the specific range, i.e., 0.0010 or less, as
apparent from FIGS. 9 and 10 and the values of Z in Table 2. By contrast,
comparative samples E and F do not satisfy requirement (A) or (B)
described hereinabove as apparent from the refractive index distribution
curves shown in FIGS. 11 and 12 and from the values of X and Y shown in
Table 2. The other comparative sample G satisfies requirements (A) and (B)
as seen from the refractive index distribution curve shown in FIG. 13 and
from the values of X and Y in Table 2, but the refractive index difference
Z between the refractive index value (a) corresponding to the maximum peak
and the refractive index value (a') corresponding to the other peak is
above 0.0010. That is, sample G does not satisfy requirement (C) described
hereinabove.
(Preparation of Photosemiconductor Device)
Using each of the seven kinds of powdery epoxy resin compositions (A to G),
a photosemiconductor device was prepared by actually subjecting an area
sensor, which is an image-pickup solid element, to direct molding at
150.degree. C. for 6 minutes, followed by postcure at 150.degree. C. for 3
hours. Using this photosemiconductor device, a camera was constructed.
Upon this camera, intense parallel rays of light (luminous intensity: 10
candelas) were allowed to strike at a right angle, and images taken at an
iris of f-32 were projected on a display. As a result, the four kinds of
cameras constructed in Examples respectively using compositions A to D
gave images free from optical unevenness as shown in Table 2 (Optical
unevenness A). By contrast, in the case of the three kinds of cameras of
Comparative Examples constructed by using compositions E to G,
respectively, optical unevenness was observed on the images with part of
the images having a striped pattern.
Furthermore, using each of the runner-shaped plates (thickness 3.0 mm,
width 5 mm) which remained in the runner part of the mold after the direct
molding described above, occurrence of optical unevenness was examined as
follows. That is, a runner-shaped plate which had a surface polished to a
surface roughness of 1.5 .mu.m or less and had a part curved at
120.degree. was placed on a molded area sensor which was an solid state
image forming element of the type having 380,000 picture elements per 1/2
inch and which had been incorporated into a camera, and then intense
parallel light rays were allowed to strike upon the plate at a right angle
to examine the resulting images for a striped pattern at an iris of f-32.
In view of the fact that sample polymers formed in the runner part were as
thick as 3.0 mm and were hence more apt to cause a striped pattern, this
optical unevenness test is more severe than the above-described optical
unevenness evaluation and can be thought to be a test whether the sample
would be applicable to future solid state image forming elements expected
to have an increased number of picture elements. As a result, the resin
plates of Examples 1 and 3 obtained from the above- described epoxy resin
compositions A and C, respectively, caused no striped pattern on the
images taken by the cameras, i.e., the two resin plates were free from
optical unevenness, while the resin plates of Examples 2 and 4 obtained
from compositions B and D, respectively, caused striped patterns to a
slight degree, as shown in Table 2 (Optical unevenness B). In contrast
thereto, all of the resin plates of Comparative Examples respectively
obtained from compositions E to G caused striped patterns.
While the invention has been described in detail and with reference to
specific embodiments thereof, it will be apparent to one skilled in the
art that various changes and modifications can be made therein without
departing from the spirit and scope thereof.
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